1. Field of the Invention
The present invention relates generally to lighting systems which are used in photographic applications, such as the filming of motion pictures. More particularly, the present invention relates to color effects lighting filters and filtering systems which are used to modify and control the quality and character of the light that is presented to the camera and film emulsion.
2. Description of Related Art
It is well-known that lighting plays an important role in still photography and in the filming of motion picture scenes. Much time is spent in selecting the type of light(s) and in controlling the lighting color temperature, intensity and quality in order to achieve desired images on film. The selection and control of lighting has been, and continues to be, a complex art. Although there are guidelines which can be used to generally predict what image will be recorded on a given film for different lighting conditions, the complex interaction of light from numerous sources in a scene can produce final color images on film which are often times unexpected and undesirable. As a result, even the most skilled cameraman or lighting technician must rely on lighting meters, trial and error testing, and a great deal of experience to achieve a lighting environment which produces desired film images.
Using colored filters to control the intensity and color of light which reaches the photographic film in the motion picture camera has been traditionally divided into two basic disciplines. The first involves filtering light in the image-forming optical path. This type of filter is typically referred to as a "lens filter." Lens filters are placed either directly before or directly behind the lens. They provide the cameraman or color lab technician with the means of accurately controlling the color and intensity of light presented to the film emulsion. A common type of colored lens filter is the color conversion filter. Color conversion filters convert the color quality of a light source so that it matches the color response for which the film has been designed. For example, if tungsten or incandescent light is used with a daylight-balanced film, a blue filter is placed before the lens. Likewise, if daylight illumination is used with tungsten-balanced film, an amber filter is recommended.
Other colored lens filters include light balancing filters, neutral density filters, color compensating filters, and special purpose filters. Light balancing filters perform the same function as color conversion filters except that finer discreet increments are used. For example, bluish filters are used to raise the light-source color temperature in degrees kelvin, while yellowish filters are used to decrease the light source color temperature. Neutral density filters are used to reduce the overall level of the light intensity. Color compensating filters differ from color conversion, light balancing and neutral density filters in that they are designed to specifically control the primary red, blue or green components of the spectrum. These color compensating filters are primarily used in the image-forming path to provide minor color correction or to adjust for minor variations in film balance due to manufacturing tolerances or conditions of use, such as storage, exposure, processing and the like.
Color compensating filters are commercially available in six colors--red, green, blue, cyan, magenta and yellow. Red, green and blue primary filters transmit their own primary component while absorbing portions of the other two primary components. Cyan, magenta and yellow secondary filters absorb portions of their respective red, green and blue complimentary component while transmitting the other two. Each color has increasing density values ranging from 0.025 to 0.50. These values refer to the effective density, as measured at the attenuated complimentary color(s), minus the density of its own transmitted color(s). As a result, for example, the density value for a yellow color compensating filter refers to the difference between the effective density of its attenuated blue transmission minus the averaged effective density of its green plus red (yellow producing) transmission.
The final principal type of colored lens filter is the special purpose filter. This type of lens filter typically includes filters for controlling the tonal rendering of colored objects for black and white photography, as well as filters used for very specific laboratory or industrial applications. As a group, colored special purpose filters are limited to an eclectic assortment of colors sharing little, if any, systematic relationship.
Although lens filters are well-suited for their intended purposes, a principal drawback of such filters is that they affect all of the light which enters the camera lens. This can be a problem, especially when filming motion picture scenes where there are multiple sources of light. For example, an interior scene filmed with tungsten-balanced film might be lit by both a tungsten light and daylight coming through a window. An amber lens filter could be used to convert the window-daylight to the tungsten balance of the film. However, the amber lens filter would render the interior tungsten light as distinctly orange. As is apparent, the potential for such color conflicts increases rapidly as the number and type of different light sources in a scene increases.
The second method for controlling the color and intensity of light reaching the film is to filter the light at its source. Such source filters are commonly referred to as "lighting filters". Exemplary lighting filters include color conversion filters, light balancing filters, neutral density filters, color compensating filters and color effects filters. The color conversion, light balancing and neutral density lighting filters are much the same as the color conversion, light balancing, and neutral density lens filters. They are used mainly to overcome the above-described problems associated with lens filters when multiple light sources of different color quality or intensity are present in a scene.
Color compensating filters for lighting are principally magenta and green types which have been limited to four densities (0.04, 0.075, 0.15, and 0.30). These filters were introduced in the early 1980's specifically for color-correcting fluorescent and industrial discharge lights. Color effects filters are generally the same types as have been used conventionally for theatrical and stage performance purposes. These types of filters, commonly called "party color gels," have been generally designed for aesthetic stage purposes without prior consideration being given to the technical requirements of recording images on photographic film.